Frank Guernsey noticed the gunboat as a dot on the horizon. Before long, it was circling the sailor like a shark moving in for the kill.

The boat flew no flags and its crew, which remained out of sight, made no attempt to contact Guernsey, nor did it respond to his calls on the radio.

All Guernsey could make out were the gun turrets on the deck.

Alone in his 24-foot sailboat, he was understandably alarmed. He hadn't seen another boat for weeks. He hadn't seen any other people for months.

Having left Redondo Beach King Harbor late last September, he had made it safely--though not without incident--to Cape Horn, a notoriously stormy region that has torn apart many a larger boat, on Dec. 31.

The rest of his trip to Argentina's Mar de Plata would be clear sailing.

Or so Guernsey thought.

Was the gunboat a modern-day pirate ship, out to plunder this apparently lost soul?

Guernsey tried repeatedly to contact the vessel on his radio.

"Where's the camaraderie?" Guernsey asked, his voice coming in clearly on his videotape of the incident. "I don't want no trouble."

Reduced nearly to skin and bones during his long journey, battered and bruised by fierce storms that walloped him before he reached "the Horn" at the southern tip of South America, Guernsey stood with a shotgun in one hand and a flare gun in the other.

Finally, however, the mysterious ship, and those on it, having apparently only moved in to get a closer look, began to pull away.

"I guess it's not going to be the gunfight at the OK Corral," Guernsey said.

And he kept on talking, to the birds, to himself; missing his wife, Mary; missing the booze he had polished off only a few days ago and the ketchup he had used up months ago.

"Ketchup," he said the other day from his Redondo Beach apartment, recalling the highlights and lowlights of the marathon of a solo sailing trip he recently completed. "I didn't have the ketchup. I really missed the ketchup."

Guernsey was no stranger to sailing alone. He had made it to Lahaina, Maui, in 27 days; to Papeete, Tahiti, in 47 days, and to Aburatsubo, Japan, in 87 days.

But his latest journey, in a 24-foot fiberglass sailboat, bordered on the ridiculous: 128 days and 15,000 miles on the water, beginning at King Harbor on Sept. 23, 1994, and culminating with his being towed into Punta del Este, Uruguay, a total wreck of a man, on Jan. 28, 1995. He may not have been the first to round Cape Horn by himself, but he is believed to be the first to willingly sail for so many days without making landfall.

"If I hadn't done those other trips, this trip . . . I couldn't have made it," Guernsey said, still a little shaky. "I shouldn't have made it anyway. This trip shouldn't have been done. I've done four, each time I went further. This time I went too far."

Perhaps, but at least he made it back. He was 30 pounds lighter--having dropped from 170 to 140 pounds--and had a mending gash on his head and three broken ribs, but he was back in one piece.

Twice he survived days-long storms with 70-knot winds that relentlessly hammered his small motorless boat, Cestus.

Had it not been for his automatic steering device, which maintained the course Guernsey set, allowing him to leave the tiller and secure himself inside the small cabin, he probably would not have made it.

In one incident, Guernsey, 53, was pitched from his berth and nearly knocked unconscious.

"For three days I was stranded in one place with currents running in all directions. It was the worst storm possible, right here," he said, pointing to an area on his chart somewhere deep in the South Pacific. "But it wasn't. Down here (farther down on the chart) it was the ultimate storm. I bumped my head and blood was shooting out. I had a lot of problems. The boat pitched me out of the quarter berth and I hit my head on a pointed edge."

The rib injury--he was nearly impaled on a piece of steel equipment--occurred during yet another storm.

"There were times the ocean was so big . . . it hits you like a hammer," Guernsey said. "And in a small boat you wonder how it's going to hold together."

His boat shouldn't have held together in 70-knot winds, experts say.

"No boat that size is built to make that kind of a trip," said Scott Thomas, manager at King Harbor Marine Center, which helped Guernsey outfit his craft. "It shouldn't have held together in those winds."

Why then did Guernsey attempt such a voyage?

Guernsey, an insurance salesman, didn't have an answer, other than that he decided to do it five years ago and felt compelled to follow through with his "commitment."

"He likes to live life on the edge," said Mary, who added that she is on edge throughout her husband's every trip.